1. Field of the Invention
The present invention relates to push-button switch units for turning on and off a lamp disposed in an in-vehicle interior light assembly. More particularly, the present invention relates to push button structures attached to an operating part of a push switch.
2. Description of the Related Art
Japanese Unexamined Utility Model Registration Application Publication No. 63-45923, for example, discloses a conventional push-button switch unit in which a push button is attached to an operating part of a push switch. According to such a push-button switch unit, the operating part of the push switch is fixed to a casing, and the push button is provided with cylindrical guiding columns. The cylindrical guiding columns engage with circular guiding holes provided in an operating surface of the casing. When the push button is pressed, the operating part of the push switch is pressed such that the push switch is turned on or off.
In such a conventional structure in which the cylindrical guiding columns engage with the circular guiding holes, if the guiding columns are narrow in width, the guiding columns may become deformed if the push button is pressed off-center, that is at a position which deviates from the center of the push button. This in turn may cause the push button to move downwardly in a tilted or skewed state instead of a state aligned longitudinally with the guiding columns. Such tilted or skewed movement may thus increase the frictional resistance between the guiding columns and the guiding holes. In such a case, a smooth switch operation cannot be performed. On the other hand, because the push button is formed of a synthetic resin and is fabricated by injection molding, if the width (radius) of the guiding columns is increased, depressions, also known as sink marks, may be formed in sections of the top surface of the push button below which the guiding columns are disposed. This is problematic in that the product value is deteriorated.